Network security starts from authenticating any user. Once authenticated, firewall enforces access policies such as what services are allowed to be accessed by the network users. Though effective to prevent unauthorized access, this component fails to check potentially harmful contents such as computer worms being transmitted over the network. An intrusion prevention system (IPS) helps detect and prevent such malware. IPS also monitors for suspicious network traffic for contents, volume and anomalies to protect the network from attacks such as denial of service. Communication between two hosts using the network could be encrypted to maintain privacy. Individual events occurring on the network could be tracked for audit purposes and for a later high level analysis.

Wide-area networks also operate over a variety of wireless media. There are 4 steps to creating a network
1.Choose your wireless equipment
2.Connect your wireless router
3.Configure your wireless router
4.Connect your computers

And as said by kawalya, Network security is a vast subject.